Method and apparatus for generating layout regions with local preferred directions

ABSTRACT

Some embodiments of the invention provide a method for defining wiring directions in a design layout having several wiring layers. The method decomposes a first wiring layer into several non-overlapping regions. It assigns at least two different local preferred wiring directions to at least two of the regions. In some embodiments, the method decomposing the first wiring layer by using the vertices of items in the layout to decompose the layout. In some of these embodiments, the items include macro blocks. The method of some embodiments also identifies several power via arrays on the first wiring layer, and identifies a local preferred wiring direction based on the arrangement of the power via arrays on the first wiring layer.

CLAIM OF BENEFIT TO PRIOR PROVISIONAL APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication 60/577,434, filed on Jun. 4, 2004.

BACKGROUND OF THE INVENTION

An integrated circuit (“IC”) is a semiconductor device that includesmany electronic components (e.g., transistors, resistors, diodes, etc.).These components are often interconnected to form multiple circuitcomponents (e.g., gates, cells, memory units, arithmetic units,controllers, decoders, etc.) on the IC. An IC also includes multiplelayers of metal and/or polysilicon wiring that interconnect itselectronic and circuit components. For instance, many ICs are currentlyfabricated with five metal layers. In theory, the wiring on the metallayers can be all-angle wiring (i.e., the wiring can be in any arbitrarydirection). Such all-angle wiring is commonly referred to as Euclideanwiring. In practice, however, each metal layer typically has one globalpreferred wiring direction, and the preferred direction alternatesbetween successive metal layers.

Many ICs use the Manhattan wiring model that specifies alternatinglayers of horizontal and vertical preferred direction wiring. In thiswiring model, the majority of the wires can only make 90° turns.Occasional diagonal jogs are sometimes allowed on the preferredhorizontal and vertical layers. Standard routing algorithms heavilypenalize these diagonal jogs (i.e. assess proportionally highrouting-costs), however, because they violate the design rules of theManhattan wiring model. Some have recently proposed ICs that use adiagonal wiring model to provide design rules that do not penalizediagonal interconnect lines (wiring). Interconnect lines are considered“diagonal” if they form an angle other than zero or ninety degrees withrespect to the layout boundary of the IC. Typically however, diagonalwiring consists of wires deposed at ±45 degrees.

Typical Manhattan and diagonal wiring models specify one preferreddirection for each wiring layer. Design difficulties arise when routingalong a layer's preferred direction because of obstacles on these wiringlayers. For example, design layouts often contain circuit components,pre-designed circuit blocks, and other obstacles to routing on a layer.Such obstacles may cause regions on a layer to become essentiallyunusable for routing along the layer's single preferred direction.

An example that shows obstacles that cause regions on a design layout tobecome unusable for routing is illustrated in FIG. 1. This figure showstwo wiring layers that each have two routing obstacles 115 and 120. Oneof the layers has a horizontal preferred direction; the other layer hasa diagonal preferred direction. The obstacles 115 and 120 cause tworegions 105 and 110 to become unusable for routing on both of theselayers. Therefore, both the Manhattan and diagonal wiring modelstypically waste routing resources on the layers of a design layout.

Accordingly, there is a need in the art for a wiring model that allowsManhattan and diagonal wiring and recaptures the routing resources lostbecause of obstacles on a wiring layer. More generally, there is a needfor a route planning method that maximizes the routing resources on eachparticular layer.

SUMMARY OF THE INVENTION

Some embodiments of the invention provide a method for defining wiringdirections in a design layout having several wiring layers. The methoddecomposes a first wiring layer into several non-overlapping regions. Itassigns at least two different local preferred wiring directions to atleast two of the regions. In some embodiments, the method decomposingthe first wiring layer by using the vertices of items in the layout todecompose the layout. In some of these embodiments, the items includemacro blocks. The method of some embodiments also identifies severalpower via arrays on the first wiring layer, and identifies a localpreferred wiring direction based on the arrangement of the power viaarrays on the first wiring layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of theinvention are set forth in the following figures.

FIG. 1 illustrates an example that shows obstacles that cause regions ona design layout to become unusable for routing is illustrated in.

FIG. 2 illustrates an example of a design layout with severaldifferently shaped local preferred direction (LPD) regions according tosome embodiments of the invention.

FIG. 3 illustrates another example of a wiring layer with severaldifferently shaped LPD regions (LPDRs) according to some embodiments ofthe invention.

FIGS. 4A and 4B provide examples that illustrate the advantage of LPDwiring model in allowing routing resources normally lost due toobstacles on a wiring layer to be recovered.

FIG. 5 illustrates an example of such a joining model of someembodiments.

FIG. 6 illustrates another example of a joining model.

FIGS. 7 and 8 illustrate examples of regions that are between macros orbetween macros and the layout boundary and that would benefit from LPDwiring.

FIG. 9 illustrates an auto-LPDR generation process that is used by someembodiments to generate LPDRs in a layout.

FIG. 10 illustrates an example of a decomposition operation on a layerwith a horizontal global preferred direction.

FIG. 11 illustrates a 45° LPD for an LPDR that is defined between twomacro blocks that are diagonally offset from each other.

FIG. 12 illustrates the elimination of several candidate LPD regions,which were created in the tessellation illustrated in FIG. 10.

FIG. 13 presents an example of an LPDR that is created on a layerbetween two macros.

FIG. 14 illustrates an example of a pin adjustment operation thatmodifies the shape of an LPDR.

FIG. 15 illustrates an example that shows the use of the corridorcreated by the adjustment for a via access to the pin. For thismodification,

FIG. 16 illustrates an example of how some embodiments allow access tothe pin through a 45° jog into the modified LPDR, a vertical traversalthrough this LPDR, and then traversing back in the 45° direction afterleaving the LPDR.

FIG. 17 illustrates another example of the pin adjustment operation.

FIGS. 18-21 illustrate examples of impermeable boundaries betweenregions on a layer and examples of eliminating such boundaries byreshaping the regions.

FIG. 22 illustrates an example of a boundary adjustment operation.

FIGS. 23-25 illustrate examples extensions of LPDRs.

FIG. 26 illustrates a process that the LPDR generator of someembodiments uses to create LPDRs between power via arrays on diagonalwiring layers.

FIG. 27 illustrates an example of creating LPDRs about power structures.

FIG. 28 illustrates the merging of the two LPDRs and to define a newLPDR.

FIG. 29 illustrates an example of an alternative embodiment of theinvention.

FIG. 30 conceptually illustrates a computer system with which someembodiment of the invention are implemented.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous details are set forth for purposeof explanation. However, one of ordinary skill in the art will realizethat the invention may be practiced without the use of these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order not to obscure the description of theinvention with unnecessary detail.

Some embodiments of the invention provide one or more Electronic DesignAutomation (EDA) tools that use a Local Preferred Direction (LPD) wiringmodel. An LPD wiring model allows at least one wiring layer to haveseveral different local preferred directions in several differentregions of the wiring layer.

Some embodiments provides a method for defining wiring directions in adesign layout having several wiring layers. The method decomposes afirst wiring layer into several non-overlapping regions. It assigns atleast two different local preferred wiring directions to at least two ofthe regions. In some embodiments, the method decomposing the firstwiring layer by using the vertices of items in the layout to decomposethe layout. In some of these embodiments, the items include macroblocks. The method of some embodiments also identifies several power viaarrays on the first wiring layer, and identifies a local preferredwiring direction based on the arrangement of the power via arrays on thefirst wiring layer.

Several features of the invention will be discussed below in Section II.However, before this discussion, Section I provides examples of LPDwiring models of some embodiments of the invention.

I. LPD Overview A. Definitions

Several embodiments of the invention provide a router that routes a setof nets in a region of an integrated circuit (“IC”) layout. Each routednet includes a set of routable elements in the IC-layout region. Theroutable elements are pins in the embodiments described below, althoughthey might be other elements in other embodiments. The routes defined bysome embodiments have “diagonal” edges. In some embodiments, a diagonaledge typically forms an angle other than 0° or 90° with respect to thelayout's Cartesian coordinate axes, which are often parallel with thelayout's boundary and/or the boundary of the layout's expected IC. Onthe other hand, a horizontal or vertical edge typically forms an angleof 0° or 90° with respect to one of the coordinate axes of the layout.The horizontal and vertical directions are referred to as the Manhattandirections.

Given a design layout with routing layers, some embodiments describe thewiring model of a layout in terms of (1) several wiring layers, (2) aglobal preferred direction D_(L) for each layer L, and (3) apotentially-empty set of LPDs for each wiring layer L. Some embodimentsdefine a “preferred” direction as the direction that a majority of thewires are laid out in a region. Some embodiments further quantify thisamount in terms of percentages or amount of the wiring. For example,some embodiments define the preferred direction of a layer as thedirection for at least 50% of the wires (also called interconnect linesor route segments) on the layer. Other embodiments define the preferreddirection of a layer as the direction for at least 1000 wires on thelayer.

Some embodiments of the invention use a five-layer wiring model thatspecifies the following global preferred directions: horizontal wiringon wiring layer 1, vertical wiring on wiring layer 2, horizontal wiringon wiring layer 3, +45° diagonal wiring on wiring layer 4, and −45°diagonal wiring (also referred to as 135° or D135 wiring) on wiringlayer 5. One of ordinary skill will realize that other embodimentsspecify the global wiring directions differently or use a differentnumber of wiring layers.

On a particular layer, a region is called an LPD region (or an LPDR)when the region has a local preferred wiring direction that is differentthan the global preferred wiring direction of the particular layer. Inaddition to the global preferred direction D_(L), some embodimentsdefine for each wiring layer L (1) at least 4 pitch values for usewhenever a global or local preferred direction can be 0°, 45°, 90°,135°; and (2) a possibly empty set of data tuples that represent regionson the layer that might have a local preferred direction that differsfrom the global preferred direction D_(L) of the layer.

The pitch values describe the track pitch along a global or localpreferred direction. In some embodiments, pitch values may change fromlayer to layer. Also, in some embodiments, each region's particulartuple t includes an “octangle” O_(t) that represents the shape of theparticular region, and a direction d_(t) that represents the localpreferred direction (i.e., 0°, 45°, 90°, 135°) of the particular region.Some embodiments allow a region's LPD d_(t) to be the same direction asthe global one.

An octangle in some embodiments is a data structure that is useful fordesign layouts that have items with horizontal, vertical, and/or ±45°directions. Specifically, in these embodiments, an octangle represents aconvex geometric shape in terms of eight values, X_(LO), y_(LO), S_(LO),t_(LO), X_(HI)y_(HI), S_(HI), and t_(HI). These eight values defineeight half-planes in two coordinate systems, where one coordinate systemis a Manhattan coordinate system that is formed by an x-axis and ay-axis, and the other coordinate system is a 45°-rotated coordinatesystem that is formed by an s-axis and a t-axis. The s-axis is at a 45°counterclockwise rotation from the x-axis, while the t-axis is at a 135°counterclockwise rotation from the x-axis. In the layouts of someembodiments, horizontal lines are aligned with the x-axis, verticallines are aligned with the y-axis, 45° diagonal lines are aligned withthe s-axis, and −45° diagonal lines are aligned with the t-axis.

Octangles are further described in U.S. patent application Ser. No.10/443,595 entitled “Method and Apparatus for Representing Items in aDesign Layout,” which published as U.S. Published Patent Application2004-0225983A1. This patent application is incorporated herein byreference. In the description below, both the wiring and non-wiringgeometries of the design layout are convex shapes, or can be decomposedinto convex shapes, that have horizontal, vertical, and ±45° sides. Oneof ordinary skill will realize, however, that some embodiments might usethe octangle data structure in cases where the wiring or non-wiringgeometries are more restricted.

Some embodiments impose several consistency requirements on an LPDdescription. For instance, some embodiments require each LPD region tobe entirely within the chip area. Also, in some embodiments, differentLPD regions on a given layer can abut only at their boundary. Inaddition, in some embodiments, all LPD regions are non-degenerate, i.e.they contain at least one interior point.

Careless definition of LPDs can lead to curious consequences like aseparated island on a plane that allows almost no wiring to enter orleave. Since EDA tools typically provide no intelligence about theintention or suitability of such a description, some embodiments of theinvention implement an additional plausibility analysis as a separatechecking stage that can be called from a Graphical User Interface (GUI)or a text-based interface (such as the Python Interface) in an initialplanning stage.

A macro block is a complex pre-designed circuit block that is used in alayout. Examples of such blocks include IP Blocks, RAM cells, etc.

B. Examples

An example of a design layout with several differently shaped LPDregions according to some embodiments of the invention is illustrated inFIG. 2. This example shows a wiring layer 200 having a 45° globalpreferred direction, an octagonal region 205 having a −45° localpreferred direction, an octagonal region 210 having a horizontal (0°local preferred direction, and a rectangular region 215 having avertical (90° local preferred direction.

FIG. 3 illustrates another example of a wiring layer with severaldifferently shaped LPD regions according to some embodiments of theinvention. This example shows a wiring layer 300 having a 90° globalpreferred direction. The layer 300 has four LPD regions having differentshapes and different local preferred directions. In the center of thelayer 300 is an octagonal LPD region 305 having a −45° local preferreddirection. Adjacent to the lower-left side of region 305 is arectangular LPD region 310 having a 45° local preferred direction.Adjacent to the upper-left side of region 305 is a hexagonal LPD region315 having a 60° local preferred direction. Adjacent to the right sideof region 305 is a square LPD region 320 having a horizontal) (0° localpreferred direction. This example illustrates the flexibility of the LPDwiring model when designing a wiring layer with different shaped LPDregions having different local preferred directions.

The examples illustrated in FIGS. 2 and 3 present simple cases of theLPD wiring model in a design layout. However, these examples do notillustrate any macros or other obstacles to the wiring on a layer. Oneof the advantages of the LPD wiring model is that it allows routingresources normally lost due to obstacles on a wiring layer to berecovered. FIGS. 4A and 4B provide examples that illustrate thisadvantage.

Specifically, FIG. 4A illustrates a wiring layer 400 having a diagonalglobal preferred direction. This wiring layer includes a column of powervia arrays 405, an IP Block 410, a set of memory cells 415, and two pins420 and 425. FIG. 4A also illustrates dotted lines that representexamples of diagonal wiring on the layer. The power stripe 405, IP Block410, and the set of memory cells 415 are all obstacles to wiring on thewiring layer. For instance, as shown in FIG. 4A, a problem arises whenpins 420 and 425 need to be connected to each other or to other pins, asthe diagonal wiring that connects to pin 420 is obstructed by the powervia arrays 405 while the diagonal wiring that connects to pin 425 isobstructed by the IP block 410.

In order to solve these routing problems, some embodiments define LPDRsabout these obstacles with the LPDs of these regions different than theglobal preferred direction of the layer. FIG. 4B illustrates examples ofsuch LPDRs. Specifically, this figure illustrates LPDRs 440 that aredefined between the power via arrays and that have a horizontal (0°)LPD. Instead of defining an LPDR between each pair of the adjacent powervia arrays, some embodiments define just one LPDR (with a horizontalLPD) that covers all the aligned power via arrays. This LPDR will havecertain regions (i.e., the regions where the power via arrays exist)blocked for routing. These embodiments define only one LPDR in order tooptimize the runtime processing of the LPDRs, as each LPDR takes upmemory and computational resources.

FIG. 4B also illustrates LPD regions 435 that are between the RAM blocks415 and that have a vertical (90°) LPD. In addition, an LPD region 430having a vertical (90°) local preferred direction is defined between theright side of the IP Block 410 and the right boundary of the wiringlayer, while an LPD region 445 having a horizontal (0°) Local preferreddirection is defined between the top side of the IP Block 410 and thetop boundary of the wiring layer. The boundary between LPDR 430 and LPDR445 is defined as a 45° diagonal line in order to increase the capacityof the wiring between two such regions. Defining such boundaries and theadvantages of such boundaries will be further described below.

The LPD regions illustrated in FIG. 4B allow wiring that was previouslyobstructed to now traverse around the obstacles by routing through theseLPD regions along their LPDs. For instance, as shown in FIG. 4B, pins420 and 425 can now be connected through a set of interconnect linesthat traverse along the global 45° direction, traverse through the LPDR440 in the horizontal direction, traverse again along the global 45°direction, and then traverse through the LPDR 445 in the horizontaldirection.

C. Joining routes at LPD borders

A common issue to address in LPD routing is how to join together routesegments that traverse two different regions with two different LPDs onthe same layer. Some embodiments of the invention join route segmentstogether along a region that is neither parallel nor perpendicular toeither route segment. FIG. 5 illustrates an example of such a joiningmodel of some embodiments. In this figure, horizontal tracks 505 arelocated in a region with a horizontal local preferred direction, whilevertical tracks 510 are located in a region with a vertical localpreferred direction. As shown in FIG. 5, horizontal and vertical tracksare joined together along a diagonal region 520, which is a diagonalline in this example.

FIG. 6 illustrates another example of such a joining model. In thisfigure, +45° tracks 605 are located in a region with a +45° localdirection, while −45° tracks 610 are located in a region with a −45°local direction. As shown in FIG. 6, 45° and −45° tracks are joinedtogether along a vertical region 620, which is a vertical line in theexample. Some embodiments manifest such joining models in terms ofboundaries between the regions, as further described below in SectionII.

D. Pitch

Some embodiments allow each LPDR to have its own set of pitch values.Other embodiments define a different pitch for each possible routingdirection of each wiring layer. For instance, some embodiments define atleast four (4) pitch values for each wiring layer, with one pitch valuefor each standard direction (horizontal, vertical, 45°, and)135°. Insome embodiments, the distance between each track in each LPD region isset according to the pitch value corresponding to the routing directionin that region.

In some embodiments, the distance between any two parallel tracks is aninteger multiple of the pitch, even when the two parallel tracks are indifferent LPDRs. Offset is the coordinate at the center of a routingtrack (e.g., it is the x-coordinate for vertical tracks). The offset ofthe tracks can be defined for each LPD or can remain undefined to belater determined by the detailed router. In either case, the trackoffsets are defined globally for each wiring direction on a layer. Thus,in some embodiments, there is a common offset for all parallel trackswithin all LPD regions within a particular layer.

Pitches and offsets may vary from layer to layer. If the pitch for aparticular region is left undefined, its value is estimated byapplications (e.g., global and detailed routers). Some embodimentsperform this estimation based on common utility functions that aredependent on minimum size net class and width/spacing of this net class.For example, if just one pitch is defined for a Manhattan direction X,the pitch for the other Manhattan direction Y is automatically estimatedwith the same value by all applications. The same applies for bothdiagonal directions. This means that if just the X-pitch is defined, theY-pitch is defaulted to the same value as X-pitch. In some embodiments,the two diagonal pitches are derived from technology design rules, e.g.,from the minimum spacing and width of the typical nets.

II. LPD Region Generation

Some embodiments of the invention include an LPDR generator thatdesignates regions on one or more layers as LPD regions. In someembodiments, the LPDR generator automatically detects LPDR candidatesand designates some of these candidates as LPD regions. In some of theseembodiments, the LPDR generator also provides the designer with agraphical user interface that allows the designer to specify LPD regionsand to modify the attributes (e.g., boundaries and LPDs) of theseregions. In other embodiments, the LPDR generator does not perform anyautomatic detection and designation of LPDRs, but instead only providesthe designer with a GUI that allows the designer to specify and modifyLPDRs. Also, some embodiments allow a user to define and manipulateLPDRs and LPDs through text-based interfaces, such as a PythonInterface.

The auto-LPDR generator of some embodiments is intended to make use ofLPDRs to increase the routing resources without forcing the user tounderstand and create LPDRs. As discussed above, LPD creation targetsregions the lack routing resources along the global preferred wiringdirection of the layer. Such regions typically exist in the alleysbetween closely placed macros and/or between a macro and the layout'sboundary. Also, such regions can be defined between power via arraysused to distribute power in the layout. Sub-section 1 below firstdescribes defining LPDRs based on macros, and then sub-section 2describes defining LPDRs between power via arrays. It should be notedthat some embodiments first define LPDRs between the power via arrays,and then define LPDRs based on macros. Alternatively, some embodimentdefine these LPDRs together.

A. Macros

FIGS. 7 and 8 illustrate examples of regions that are between macros orbetween macros and the layout boundary and that would benefit from LPDwiring. Specifically, FIG. 7 illustrates two macro blocks 715 and 720 ona layer with a horizontal global preferred direction. As shown in thisfigure, the region 705 between the two macros and the region 710 betweenthe macro 715 and the layer boundary provide small amounts of routingspace, which are not particularly useful given the horizontal globalpreferred direction of the wiring on the layer. FIG. 8 illustrates aregion 805 between a macro 810 and the boundary of a layer with a 45°diagonal wiring. Like the regions 705 and 710 of FIG. 7, the regions 805provides a small amount of routing space that is not particularly usefulgiven the 45° global preferred direction of the wiring on the layer.Hence, to make use of regions 705, 710, and 805, the preferred wiringdirections of these regions should be specified differently from theglobal preferred wiring direction of their layer.

FIG. 9 illustrates an auto-LPDR generation process 900 that is used bysome embodiments to generate LPDRs in a layout. This process: (1)identifies candidate regions, (2) designates some or all of thecandidate regions as LPDRs, (3) adjusts the LPDRs for pin access, and(4) modifies LPDRs to improve routability between LPDRs and betweenLPDRs and non-LPDR regions on a layer. This process is described interms of several examples that relate to LPDR generation on layers withManhattan global preferred directions.

As shown in FIG. 9, the process 900 starts by selecting (at 905) alayout layer. The process then decomposes (at 910) the layout layer intoseveral regions. In some embodiments, the process decomposes theselected layout layer by projecting rays from the corner vertices of theoutline of the macro blocks on the selected layer. The outlines of themacro blocks might have been defined prior to 910 or they might bedefined at 910 based on the shape and structure of the content of themacro blocks.

The projected rays are in the direction of the global preferred wiringdirection of the selected layer. FIG. 10 illustrates an example of adecomposition operation on a layer with a horizontal global preferreddirection. In this example, the layer has six macros 1005. Rays areprojected from the vertices of these six macros in the horizontal globalpreferred direction. These projections define thirteen candidate LPDregions 1010.

After 910, the process then selects (at 915) one of the contiguousregions created through the decomposition. It then determines (at 920)whether it should designate the selected region as an LPDR for aparticular local preferred direction. In some embodiment, the processmakes this determination by applying a set of geometric criteria. Thecriteria are meant to ensure that the designation of the selected regionas an LPDR does not remove routing resources from a layer, that usableresources are created by the local preferred direction of the LPDR, andthat sufficient additional resources get created in order to justify theextra runtime and/or memory cost of including an LPDR.

In some embodiments, the criteria for defining LPDRs on a layer with ahorizontal global preferred direction is:

-   -   W_(Max)≧Width of Region≧W_(Min), and    -   Length of Region≧L_(Min),        where the width of the region is in the horizontal direction,        the length of the region is in the vertical direction, W_(Max)        and W_(Min) are upper and lower limits on the width of the        region, and L_(Min) is a lower limit on the length of the        region. The lower limit on region width ensures that the amount        of additional vertical or diagonal resource is worth the cost of        LPDRs. The upper limit on region width ensures that significant        horizontal resources are not lost. Finally, the lower limit on        the region's length ensures that the region is not too short, as        vertical or diagonal tracks that are smaller than some length        might not be of any significant use. This way the additional        vertical or diagonal routes will have significant movement along        the vertical or diagonal direction.

In some embodiments, the criteria for defining LPDRs on a layer with avertical global preferred direction is:

-   -   L_(Max)≧Length of Region≧L_(Min), and    -   Width of Region≧W_(Min).        Again, the width of the region is in the horizontal direction,        the length of the region is in the vertical direction, L_(Max)        and L_(Min) are upper and lower limits on the length of the        region, and W_(Min) is a lower limit on the width of the region.        The lower limit on region length ensures that the amount of        additional horizontal or diagonal resource is worth the cost of        LPDRs. The upper limit on region length ensures that significant        vertical resources do not get lost. Finally, the lower limit on        the region's width ensures that the region is not too thin, as        horizontal or diagonal tracks that are smaller than some length        might not be of any significant use. This way the additional        horizontal or diagonal routes will have significant movement        along the horizontal or diagonal direction. Some embodiments        define the criteria for defining LPDRs on a layer with diagonal        global preferred directions similarly.

If the process determines (at 920) that the selected region is not agood candidate for an LPDR, the process transitions to 930, which willbe described below. On the other hand, when the process determines (at920) that the selected region is a good LPDR candidate, it transitionsto 925, where it designates the selected region as an LPDR. At 925, theprocess also designates the LPD of the selected region.

For a layer that has a Manhattan global preferred direction, someembodiments define the LPD of a designated LPDR on that layer as theManhattan direction that is orthogonal to the layer's Manhattan globalpreferred direction. On a layer that has a diagonal global preferreddirection, some embodiments define the LPD of a designated LPDR on thatlayer as one of the Manhattan directions. This Manhattan direction mightbe a direction that is identified by the dimensional attributes (e.g.,orientation) of the LPDR. For instance, when the LPDR is a tall andnarrow rectangle aligned with the y-axis, the LPD direction might bedesignated as the vertical direction. Alternatively, some embodimentsdefine the LPD of an LPDR on any layer based on the dimensionalattributes of the LPDR. Also, some embodiments define the LPD of an LPDRthat is defined between two or more macro blocks based on the positionalrelationship of the macro blocks. For instance, FIG. 11 illustrates a45° LPD for an LPDR 1105 that is defined between two macro blocks 1110and 1115 that are diagonally offset from each other, because itfacilitated routing between the open areas 1120 and 1125 to reduce theimpact of the macroblocks.

FIG. 12 illustrates the elimination of several candidate LPD regions,which were created in the tessellation illustrated in FIG. 10, forfailing to satisfy the above-described width and length criteria. Inthis example, the remaining LPDRs (i.e., the LPDRs illustrated in thisfigure) all have been assigned a vertical LPD.

After 925, the process transitions to 930. At 930, the processdetermines whether it has examined all the contiguous regions created onthe selected layer by the decomposition operation at 910. If not, theprocess selects (at 915) another contiguous region, determines (at 920)whether this region should be designated as an LPDR, and (3) in case ofan affirmative determination at 920, designates (at 925) the selectedregion as an LPDR.

When the process determines (at 930) that it has examined all thecontiguous regions created on the selected layer by the decompositionoperation at 910, the process examines (at 935) each particular regionthat it designated (at 925) as an LPD region to determine whether itneeds to adjust or eliminate this region based on pins at the boundariesof the particular region.

The newly created LPDRs should not hinder pin access. Hence, the process900 needs to ensure that the LPDRs provide a safe distance for access tothe pins. Accordingly, for each particular LPDR defined at 925, theprocess initially determines (at 935) whether there is at least one pinon one side of the particular LPDR that needs to connect to another pinon another side of the LPDR. If so, the process discards the LPDR insome embodiments, as the LPDR would block the easiest way to connect thetwo pins. FIG. 13 presents an example of an LPDR 1305 that is created ona layer between two macros 1310 and 1315. On the two sides of the LPDR1305, the two macros have two pins 1320 and 1325 that need to connect.Hence, as shown in FIG. 13, the pin adjustment operation at 935 removesthe LPDR 1305 from the layout. Instead of discarding (at 935) an LPDR,the process 900 in some embodiments tries to modify (at 935) the shapeof the LPDR (e.g., tries to make the LPDR narrower or shorter as furtherdescribed below) when it determines that there is one pin on one side ofthe particular LPDR that needs to connect to another pin on another sideof the LPDR. If the modification fails to lead to an acceptablesolution, the process then discards the LPDR in some embodiments.

The process 900 also identifies (at 935) each LPDR defined at 925 thathas one or more pins on its sides even when the pins do not need toconnect across the LPDR. For each such LPDR, the process (1) changes theshape of the LPDR to create one or more open corridors for pin access,and (2) then determines whether the modified LPDR still satisfies theabove-mentioned criteria for creating the LPDR. If the modified LPDR nolonger satisfies one or more of the criteria (e.g., the modified LPDR'swidth is smaller than the required minimum width), the process discardsthe LPDR. Otherwise, the process keeps the LPDR with its modified shape.

FIG. 14 illustrates an example of a pin adjustment operation thatmodifies the shape of an LPDR. Specifically, this figure presents anexample of an LPDR 1405 that is created on a layer between two macros1410 and 1415. On one side of the LPDR 1405, the macro 1410 has a pin1420 that needs to be connected. Hence, as shown in FIG. 14, the pinadjustment operation at 935 makes the LPDR 1405 narrower (i.e., reducesits width).

Modifying the shape of an LPDR provides sufficient routing flexibilityfor accessing the pins. This leeway can be used by routes to either viaout of the layer (the way they would have done without LPDRs) or to joginto the LPDR and blend into the flow. For the LPDR modificationillustrated in FIG. 14, FIG. 15 illustrates an example that shows theuse of the corridor 1405 created by the adjustment for a via access tothe pin. For this modification, FIG. 16 illustrates an example of howsome embodiments allow access to the pin through a 45° jog 1610 into themodified LPDR 1405, a vertical traversal through this LPDR, and thentraversing back in the 45° direction after leaving the LPDR. Given thatjog 1610 is not along a the LPD of the region 1405, some embodimentsassess this jog a penalty for traversing a portion of this region alongits non-preferred direction.

The amount that a dimension of the LPDR is adjusted is dependent on thenumber of pins on the side or sides of the LPDR that are associated withthat dimension. For instance, some embodiments deduct the followingdistance D from each side of an LPDR region:

D=Max(S _(Min) ,P _(Max)*pitch*C_(Pin))

where P_(Max) is the number of pins along the edges of the LPDR, pitchis the wiring pitch along the global preferred direction, C_(Pin) is apin routing cost that is a heuristic parameter that quantifies the costof a number of tracks that have to be left aside per pin, and S_(Min) isthe minimum spacing requirement for pin access, which is defined by thedesign rules. Some embodiments drop the min-spacing requirement from theabove formula in order to simplify it as follows:

D=P _(Max)*pitch*C_(Pin)

Some embodiments might use different rules for performing pinadjustments on layers with diagonal global preferred directions than onlayers with Manhattan global preferred directions. For instance, someembodiments may choose to maintain the diagonal direction in avertically/horizontally shaped region and hence may discard an LPDR whenthere is a pin at the boundary of the LPDR.

FIG. 17 illustrates another example of the pin adjustment operation.This example is a continuation of the examples illustrated in FIGS. 10and 12. The top layout illustration in FIG. 17 presents several pins onthe sides of the macros 1005. Next, the bottom left layout illustrationin FIG. 17 shows the elimination of LPDR 1010. This LPDR was eliminatedbecause two pins 1705 and 1710 on its sides need to be connected to eachother. The bottom left layout also illustrates the narrowing of LPDRs1015 and 1020 to create corridors for accessing pins on the side ofthese two LPDRs. Finally, the bottom right layout in FIG. 17 illustratesthe elimination of the narrowed LPDR 1015 for failing to satisfy theminimum width criteria for a vertical LPDR.

After performing the pin adjustment operation at 935, the processperforms a boundary adjustment operation at 940. In some embodiments,the routability between two regions is dependent on their routingdirections and the orientation of the edge separating the two regions.Specifically, when one of the wiring directions between two regions on alayer is parallel to a boundary between the two regions, then someembodiments define the capacity at the boundary between two regions aszero. Such a boundary is referred to as an impermeable boundary betweenthe two wiring directions.

To avoid such impermeable boundaries, the process 900 performs theboundary adjustment operation at 940 that changes the boundary betweentwo regions to eliminate any impermeable boundaries between them. FIGS.18-20 illustrate examples of impermeable boundaries between regions on alayer and examples of eliminating such boundaries by reshaping theregions. Specifically, FIG. 18 illustrates a layer with a horizontalglobal preferred wiring direction and a LPDR 1805 between two macros1810 and 1815. As shown in this figure, the LPDR 1805 has a verticalLPD. The LPDR 1805 also has horizontal top and bottom sides 1820 and1825 that are parallel to the horizontal global preferred wiringdirection of the layer. Accordingly, some embodiments define thewireflow capacity across the top and bottom sides 1820 and 1825 as zero(i.e., define these sides as impermeable sides). Such a wireflowdefinition is a conservative definition as a detailed router might allownon-preferred direction jogs at such boundaries.

The permeability at the boundary of the LPDR 1805 and the region withthe global preferred wiring direction can be improved by modifying theshape of this boundary. For instance, FIG. 19 illustrates the additionof triangular crown regions 1905 and 1910 to the top and bottom sides ofthe LPDR 1805. Each triangular crown extension of the LPDR 1805 includesa 45° edge and a vertical edge. In some embodiments, the 45° edge is apermeable edge for routes to enter and exist the LPDR, while thevertical edge is an impermeable edge as it is parallel to the verticalLPD of the LPDR 1805. FIG. 19 illustrates an example of a route 1920that traverses through the LPDR 1805 through its permeable edges.

FIG. 20 illustrates the additions of alternative triangular crownregions 2005 and 2010 to the top and bottom sides of the LPDR 1805. Eachof these triangular crown extensions of the LPDR 1805 includes two 45°edges, both of which are in some embodiments, permeable edges. FIG. 21illustrates two routes 2105 and 2110 that enter the LPDR 1805 throughthese permeable edges. However, as shown in FIG. 21, the route 2105includes a non-preferred direction jog in the LPDR 1805. Hence, theadded advantage of the two extra permeable edges that are provided bythe crown extensions 2005 and 2010 come at the expense of requiring someroutes to have non-preferred direction jogs in the LPDR.

LPDR crown extensions provide well-defined bending points for theroutes. These well-defined points are only as strict as the layerdirection itself Accordingly, in some embodiments, the same kind of jogsthat can run orthogonal to a routing direction can also violate thebending points in case the benefit offsets a higher price of anon-preferred-direction jog.

Some embodiments use the following approach to modify an impermeableboundary of an LPDR on a Manhattan layer. The impermeable boundary ofthe LPDR abuts two edges of the LPDR that abut the boundary edges of thelayer or of macros on the layer. Each of these two edges is checked todetermine whether it can be extended. This involves checking the boundsof the macro's edge next to it. The end-point of the edge is termedextendible if the edge can be elongated at that end-point withoutextending beyond the macro's edge. The amount, by which the edge needsto extend for stretching up to the obstruction edge, is the ExtendLimit.The extendibility and the ExtendLimit are determined at four points,which are two endpoints of both the edges.

The following description provides an example of the stretching logicthat is performed to stretch a vertically shaped LPDR. When the LPDR canbe extended at both its left top corner and right top corner, then theprocess discards the LPDR as there was some error in its creation.Alternatively, when the LPDR can be extended at its left top corner butnot its right top corner, then the process stretches the LPDR's leftedge upwards by the minimum of the LPDR width and a maximum top stretchlimit. If the LPDR's left edge cannot be stretched by this minimumamount, then the LPDR is discarded in some embodiments.

When the LPDR can be extended at its right top corner but not its lefttop corner, then the process stretches the LPDR's right edge upwards bythe minimum of the LPDR width or a maximum top stretch limit. If theLPDR's right edge cannot be stretched by this minimum amount, then theLPDR is discarded in some embodiments. When the left and right topcorners of the LPDR cannot be extended, then the process connects theleft edge and the right edge by a 45° edge and a 135° edge respectively.The 45° and 135° edges should not exceed the top stretch limit. Iftruncated, a horizontal line should connect the 45° and 135° edges.Stretching the bottom boundary of a vertical LPDR or the right and leftsides of a horizontal LPDR follows an analogous set of operations forthe bottom, right, and left sides of an LPDR.

FIG. 22 illustrates another example of the boundary adjustmentoperation. This example is a continuation of the examples illustrated inFIGS. 10, 12, and 17. This figure illustrates the creation of crownextensions for each of the LPDRs with vertical LPDs. Crown extensions2205, 2210, and 2215 are triangular extensions extended from one side ofthe LPDR, while crown extensions 2220, 2225, and 2230 are triangularextensions extended from both sides of the LPDR. Extensions 2235 and2240 are four sided extensions that resulted because of the boundary ofthe layer or because of the minimum spacing requirement for pin access.

Some embodiments might use different rules for performing boundaryadjustments on layers with diagonal global preferred directions than onlayers with Manhattan global preferred directions. An LPDR, with aManhattan LPD and a Manhattan outline on a layer with diagonal globalpreferred wiring, is always permeable itself. However, the LPDRs createdaround it can deteriorate its permeability/routability. Accordingly, foreach macro on a diagonal layer that has LPDRs on two consecutive sides,some embodiments extend the two LPDRs to join them at the corner vertexwhere the sides meet. The modus operandi of this extension is to extendthe Manhattan bound of region-end-point to a large value, and constrainthe region with a diagonal bound. The bound is stretched diagonallyoutward from the vertex of the two consecutive sides.

FIG. 23 illustrates an example of such an extension. Specifically, thisfigure illustrates expanding two LPDRs 2305 and 2310 that abut a macro2315 to improve the routability between these LPDRs and the rest of thelayer. Such a solution might lead to odd boundaries between the LPDRs,such as the contact between LPDRs 2405 and 2410 that are illustrated inFIG. 24. This contact creates an impermeable edge 2415 between the LPDR2410 and the rest of the layer as it is parallel to the global preferredwiring direction of the layer. Such an impermeable edge is createdbecause the height of LPDR 2405 is smaller than the width of LPDR 2410.In such cases, the two LPDRs might not be extended at all, might beextended as shown in FIG. 24 but then corrected during a manual LPDRcreation by a designer, or might be extended in a manner that results inthe pentagonal shape for LPDR 2510 that is illustrated in FIG. 25.

In extending LPDRs, the boundary adjustment operation at 940 might leadto the LPDRs overlapping other LPDRs. So, after the boundary adjustingoperation at 940, the process 900 checks (at 945) all LPDRs on theselected layer to make sure that no two LPDRs overlap. When itidentifies two LPDRs that overlap, it deletes (at 945) one of them(e.g., the smaller LPDR) in the region of the overlaps. After 945, theprocess determines (at 950) whether it has examined all the wiringlayers. If not, the process returns to 905 to select another wiringlayer and then performs the subsequent operations to potentially defineone or more LPDs on this layer. When the process determines (at 950)that it has examined all the wiring layers that it needs to examine, theprocess ends.

B. Power Via Arrays

Power structures often reduce the routing resources that are availableon the wiring layers. Power via arrays are one example of such powerstructures. A power via array includes a set of vias that are used toroute power from power lines (also called power stripes) on the topmostmetal layers down into the lower metal layers. These power stripesrequire Manhattan directed wiring to access the set of vias in the powerarray. Accordingly, as discussed above, problems in routing arise whentrying to route wiring on a diagonal layer with Manhattan power stripes.As further described above, some embodiments solve this problem bydefining LPDRs with Manhattan LPDs for horizontally or verticallyaligned power via arrays.

FIG. 26 illustrates a process 2600 that the LPDR generator of someembodiments uses to create LPDRs between power via arrays on diagonalwiring layers. This process creates LPDRs starting from the top-mostdiagonal layer and moves down until it finishes with all the diagonallayers. In a layer, the process considers all the power stripes in someembodiments, while considering only power stripes greater than aconfigurable threshold size (e.g., 100 micron) in other embodiments. Theprocess ignores all diagonal power stripes. For each Manhattan powerstripe that is greater than the threshold size, the process creates anLPDR with the same outline as the stripe. The LPD of the LPDR will behorizontal for a vertically shaped LPDR, and vertical for a horizontallyshaped LPDR. For each potential LPDR, the capacity will be calculatedfor the Gcells containing the LPDR (with and without the LPDR). If theLPDR increases the capacity at least two-fold, the LPDR is added to thedatabase. Otherwise, the LPDR will be discarded.

As shown in FIG. 26, the process 2600 identifies (at 2605) the number ofrouting layers and the diagonal layers with no power stripes. Theprocess 2600 then iterates (at 2610) through the power and ground netsin the netclass database to identify each Manhattan power stripe that ison a layer above the lowest diagonal layer and that is larger than aparticular configurable threshold size. In some embodiments, thethreshold size of the Manhattan power stripe is 100 microns, althoughthis size can be redefined by a designer. Each Manhattan power stripeidentified at 2610 might be used to define an LPDR on one or morediagonal wiring layers below it, as further described below. To identifypower vias, some embodiments might represent an entire power via-stackthat includes multiple cuts as one via.

Next, at 2615, the process defines the Current_Layer as the topmostdiagonal layer. It then selects (at 2620) the nearest layer that isabove the Current_Layer and that has Manhattan power stripes. Theprocess then determines (at 2625) whether the selected layer above theCurrent_Layer has a sufficient number of (e.g., ten) Manhattan powerstripes. The number of power stripes that are sufficient is configurablein some embodiments.

If the process determines that the selected layer does not have asufficient number of Manhattan power stripes, the process transitions to2640, which will be described below. Otherwise, the process evaluates(at 2630) the outline of each particular Manhattan stripe as a potentialLPDR on the Current_Layer.

Specifically, for each potential LPDR that can be defined based on eachparticular Manhattan stripe, the process performs (at 2630) two capacitycomputations for the set of Gcells that contain the potential LPDR. Onecapacity computation is the total capacity of all the Gcells in the setwithout the potential LPDR, while the other one is the total capacity ofthese Gcells with the potential LPDR. The capacity calculation isperformed with power/ground vias taken as obstructions. When thepotential LPDR fails to increase the capacity of the set of Gcells atleast two-fold, the process does not define an LPDR. Alternatively, onthe Current_Layer, the process defines (at 2630) an LPDR based on theoutline of the particular Manhattan power stripe when the potential LPDRincreases the capacity of the set of Gcells at least two-fold.

FIG. 27 illustrates an example of creating LPDRs about power structures.Specifically, this figure illustrates a wiring layer that has a diagonalglobal preferred direction. This layer also has a region 2705 that isunderneath a vertical power stripe. Hence, as shown in FIG. 27, theregion 2705 can be defined as an LPDR that has a horizontal LPD. ThisLPD, in turn, provides horizontal routing and/or tracks that allowsdiagonal routing and/or tracks to pass through this region whileavoiding the power-via obstacles that are defined for the vertical powerstripe.

After 2630, the process 2600 examines (at 2635) any LPDRs that it justcreated at 2630 to determine whether to merge adjacent LPDRs. DefiningLPDRs for adjacent power stripes might create unusable channels betweenthe LPDRs. FIG. 28 illustrates two LPDRs 2810 and 2820 that are definedfor two different power stripes. In this example, the LPD in each LPDRis horizontal and the global preferred wiring direction of the layer is45° diagonal. As shown in this figure, the wiring that leaves the LPDR2810 that is defined for one power stripe can run into a power via stack2815 in the LPDR 2820 of the other power strip.

FIG. 28 illustrates the merging of the two LPDRs 2810 and 2820 to definea new LPDR 2830. The “merged” LPD region 2830 is defined to encompassthe region of both power stripes and has the same local preferreddirection as the LPD of the replaced LPDRs 2810 and 2820. This mergingallows the wiring to traverse efficiently across the region underneaththe power stripes without the obstruction that existed when the twoLPDRs 2810 and 2820 were separate.

Some embodiment merge power-stripe LPDRs that are closer than 10% of thestripe-width. Some embodiments perform the merging after thecapacity-increase-based LPDR filtering because they assume that a regionthat does not gain capacity from a change to its routing direction, willnot gain capacity even if merged with another LPDR. Other embodiments,however, might account for the merging while performing the capacityestimation and determining whether to define an LPDR.

In some embodiments, the merging operation merges two aligned (e.g.,horizontally aligned) LPDRs by extending one LPDR (e.g., the LPDR to theleft) towards the other LPDR (e.g., the LPDR to the right). The formulabelow quantifies the horizontal extension (HExt) of leftside LPDRtowards a rightside LPDR:

Hext=(HseparationOfStripe−viaStackOffset)mod interval,

where HSeperationOfStripe is the horizontal separation of the powerstripes, viaStackOffset is the amount of offset between the via stack inthe left stripe and the via stack of the right stripe, and interval isthe distance between the two via stacks that are part of the stripecorresponding to the left LPDR. Some embodiments put a ceiling on theextension to make sure that not more than a particular percent of thelayer is converted to LPDRs. For example, a Horizontal extension willtake place only if the value is less than the stripe's width. A valuegreater than the ceiling is ignored, as it would not be helpful to drawanything less than the horizontal value. Hence, in such cases, someembodiments do not define the LPDR that would need to surpass theceiling.

A second step after the extensions would be to check whether an LPDR hasextended into the next LPDR. If so, the merging operation merges thedefinition of the two LPDRs, provided that they pass a capacityconstraint, which will be described below. The above-described approachassumes that the via-stacks within a stripe are placed at regularintervals, that the interval remains the same for the two stripes beingconsidered, and that power-vias do not lie outside the stripes. Someembodiments incorporate a check for such requirements at the beginningof the merging operation.

As mentioned above, the merging operation at 2635 performs anothercapacity-increase-based filtering. Unaligned vias can cause the failureof capacity increase. In case of a failure, the process in someembodiments discards the merged LPDR. Instead of performing apost-processing operation to merge LPDRs for adjacent power stripes,some embodiments might generate larger LPDRs at 2630 that account forthe need to have a combined LPDR for adjacent power stripes.

After 2635, the process determines (at 2640) whether there is anydiagonal layer lower than the Current_Layer. If so, the process selects(at 2645) the next lower layer, designates this layer as theCurrent_Layer, and transitions back to 2620, which was described above.Otherwise, the process ends.

Some embodiments define LPDRs about power structures in view of certainconstraints. For instance, some embodiments do not create LPDRs aroundoverlapping power stripes. In some cases, a designer has to manuallyanalyze the LPDRs to ensure that this constraint is met. Also, asmentioned above, the LPDR generator in some embodiments first definesLPDRs about power structures and then defines LPDRs between the macros.Accordingly, the LPDR generator in some embodiments does not checkwhether the power-based LPDRs overlap any other existing LPDRs. In fact,the LPDR generator might delete all pre-existing LPDRs before creatingany power-based LPDRs on a layer.

FIG. 29 illustrates an example of an alternative embodiment of theinvention. This figure illustrates the outlines 2905 of several powerstripes on a layer. It also illustrates several LPDRs that areorthogonal to the outline of the power stripes, instead of being definedparallel and in between the stripes.

U.S. patent application entitled “Local Preferred DirectionArchitecture, Tools, and Apparatus” filed concurrently with the presentapplication, with the Express Mail Number EV454047165US, and attorneydocket number CDN.P0076, describes the GUI of the LPDR generator of someembodiments of the invention. Also, U.S. patent application entitled“Local Preferred Direction Routing,” filed concurrently with the presentapplication, with the Express Mail Number EV454047143US, and attorneydocket number CDN.P0078, describes the routing tools that can route alayout with LPDs. These applications are incorporated herein byreference. Other EDA tools can also consider layouts with LPDs. Forinstance, some embodiments might include a placer that computesplacement costs (e.g., wirelength and/or congestion costs) based on thedifferent LPDs within which the circuit modules or the pins of thesemodules fall.

III. Computer System

FIG. 30 conceptually illustrates a computer system with which someembodiment of the invention are implemented. Computer system 3000includes a bus 3005, a processor 3010, a system memory 3015, a read-onlymemory 3020, a permanent storage device 3025, input devices 3030, andoutput devices 3035.

The bus 3005 collectively represents all system, peripheral, and chipsetbuses that support communication among internal devices of the computersystem 3000. For instance, the bus 3005 communicatively connects theprocessor 3010 with the read-only memory 3020, the system memory 3015,and the permanent storage device 3025.

From these various memory units, the processor 3010 retrievesinstructions to execute and data to process in order to execute theprocesses of the invention. The read-only-memory (ROM) 3020 storesstatic data and instructions that are needed by the processor 3010 andother modules of the computer system. The permanent storage device 3025,on the other hand, is a read-and-write memory device. This device is anon-volatile memory unit that stores instruction and data even when thecomputer system 3000 is off. Some embodiments of the invention use amass-storage device (such as a magnetic or optical disk and itscorresponding disk drive) as the permanent storage device 3025. Otherembodiments use a removable storage device (such as a floppy disk orZip® disk, and its corresponding disk drive) as the permanent storagedevice.

Like the permanent storage device 3025, the system memory 3015 is aread-and-write memory device. However, unlike storage device 3025, thesystem memory is a volatile read-and-write memory, such as a randomaccess memory. The system memory stores some of the instructions anddata that the processor needs at runtime. In some embodiments, theinvention's processes are stored in the system memory 3015, thepermanent storage device 3025, and/or the read-only memory 3020.

The bus 3005 also connects to the input and output devices 3030 and3035. The input devices enable the user to communicate information andselect commands to the computer system. The input devices 3030 includealphanumeric keyboards and cursor-controllers. The output devices 3035display images generated by the computer system. For instance, thesedevices display IC design layouts. The output devices include printersand display devices, such as cathode ray tubes (CRT) or liquid crystaldisplays (LCD).

Finally, as shown in FIG. 30, bus 3005 also couples computer 3000 to anetwork 3065 through a network adapter (not shown). In this manner, thecomputer can be a part of a network of computers (such as a local areanetwork (“LAN”), a wide area network (“WAN”), or an Intranet) or anetwork of networks (such as the Internet). Any or all of the componentsof computer system 3000 may be used in conjunction with the invention.However, one of ordinary skill in the art will appreciate that any othersystem configuration may also be used in conjunction with the invention.

While the invention has been described with reference to numerousspecific details, one of ordinary skill in the art will recognize thatthe invention can be embodied in other specific forms without departingfrom the spirit of the invention. For instance, some embodiments definea crown boundary between an LPDR with a Manhattan LPD (e.g., ahorizontal direction) and an LPDR with a non-Manhattan LPD (e.g., a 45°diagonal direction) in terms of an angle that is between the Manhattanand non-Manhattan directions (e.g., a 22.5° direction). Thus, one ofordinary skill in the art would understand that the invention is not tobe limited by the foregoing illustrative details, but rather is to bedefined by the appended claims.

1-20. (canceled)
 21. A computer-implemented method of defining wiringdirections in a design layout comprising a plurality of wiring layers,the method comprising: a) identifying a first region on a wiring layercomprising a set of items, the set of items comprising a set of pins,wherein the first region comprises a first local preferred wiringdirection that is different than a second local preferred wiringdirection associated with a second region on the wiring layer; b)identifying at least one pin on the wiring layer that is adjacent to thefirst region; c) determining whether the first region increases a costassociated with routing the identified pin; and d) discarding the firstregion when the first region increases the cost associated with routingthe identified pin.
 22. The method of claim 21, wherein discarding thefirst region comprises disassociating the first local preferred wiringdirection from the first region.
 23. The method of claim 21, wherein thefirst region is discarded when modifying a shape of the first regionincreases the cost associated with routing the identified pin.
 24. Acomputer-implemented method of defining wiring directions in a designlayout comprising a plurality of wiring layers, the method comprising:a) identifying a first region on a wiring layer comprising a set ofitems, the set of items comprising a set of pins, wherein the firstregion comprises a first local preferred wiring direction that isdifferent than a second local preferred wiring direction associated witha second region on the wiring layer; b) identifying at least one pin onthe wiring layer that is adjacent to the first region; c) determiningwhether the first region increases a cost associated with routing theidentified pin; and d) modifying a shape of the first region when thefirst region increases the cost associated with routing the identifiedpin.
 25. The method of claim 24, wherein modifying the shape comprisesnarrowing the first region.
 26. The method of claim 25, wherein anamount of narrowing is based on a spacing requirement for accessing theidentified pin.